I suggest that you consider St. Thomas on the USVI. Stay at the Marriott Frenchman's Reef Hotel for luxury and a nice, white sand beach. Dive on the west side of the island with Blue Island Divers. Avoid the east side since the diving is not as nice as the west side. If you go with the guys at Blue Island, you will see the best that St. Thomas has to offer. If you want to see a huge nurse shark, ask them to take you to the Kennedy; I swear that shark is 16+ feet long! And be sure to do Flat Top: a wonderful collection of sealife all along the dive.
Some folks think that the Wreck of the Rhone on the east side is a "must do". I am not one of them. The ship is not intact and the vis can be very poor, especially after a group of inexperienced divers has kicked up all the silt!
Lots of good restaurants on ST, USVI and some nice sight seeing, to boot. The diving is not Cozumel, but it is a darn nice place for a honeymoon!
And speaking of Cozumel, Mexico: it is a great place to dive, but there are very few truly pristine white sand beaches that are convenient. The Fiesta Americana has a man-made beach that is very nice, however. Now a word to the wise: The diving there is great! You can get a package from Islandreams (on the net) that includes Continental Airlines, Fiesta Americana and The Dive Shop. The latter is right on site at the Fiesta and is a nice operation. Also, there is a decent shore dive right in front of the resort and you can get wts, tanks and other gear, if you need it, from The Dive Shop.
Scorpionfish